3D structured optical fiber pressure sensors

Pressure sensors based on fiber Bragg gratings in side-hole optical fiber enable remote monitoring of pressure at multiple points within many otherwise inaccessible environments. However, sensors fabricated from side-hole fiber drawn from a preform have limitations in their design and material composition. The design of such sensors is a compromise between achieving good sensitivity, while also minimizing splice losses due to mode-mismatch. We have developed optimized designs for pressure sensors with complex 3D structures using simulations and fabricated them within commercial step-index fibers. The fabrication uses a femtosecond laser in conjunction with selective etching to write precisely defined voids within the fiber cladding. The sensors were tested in a hydraulic system up to 600 bar and achieved a sensitivity of 0.41 pm/bar. The technique has potential for enabling pressure sensors in many types of high-performance fibers for a range of sensing applications.